U.S. patent number 9,608,443 [Application Number 14/292,304] was granted by the patent office on 2017-03-28 for energy storage system of uninterruptible power supply equipped with battery and method of driving the same.
This patent grant is currently assigned to EHWA TECHNOLOGIES INFORMATION CO., LTD.. The grantee listed for this patent is EHWA TECHNOLOGIES INFORMATION CO., LTD.. Invention is credited to Sung Won Chung, Kyung Suk Lee, Dong Hun Yum.
United States Patent |
9,608,443 |
Chung , et al. |
March 28, 2017 |
Energy storage system of uninterruptible power supply equipped with
battery and method of driving the same
Abstract
Disclosed herein are the energy storage system of an
Uninterruptible Power Supply (UPS) equipped with the battery and a
method of driving the same. The energy storage system includes a
commercial power source unit configured to supply a first power
source to a load, and the battery configured to supply a second
power source to the load. And the system monitors a power failure
state in the commercial power source unit, determines a charging
state of the battery, and controls the commercial power source unit
and the battery in response to output of monitoring or
determination, so that the first power source or the second power
source is supplied to the load. A power reservation ratio for the
use of power can be increased by reducing power used during
daytime.
Inventors: |
Chung; Sung Won (Seoul,
KR), Lee; Kyung Suk (Seoul, KR), Yum; Dong
Hun (Gyeonggi-do, KR) |
Applicant: |
Name |
City |
State |
Country |
Type |
EHWA TECHNOLOGIES INFORMATION CO., LTD. |
Seoul |
N/A |
KR |
|
|
Assignee: |
EHWA TECHNOLOGIES INFORMATION CO.,
LTD. (Seoul, KR)
|
Family
ID: |
49639386 |
Appl.
No.: |
14/292,304 |
Filed: |
May 30, 2014 |
Prior Publication Data
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Document
Identifier |
Publication Date |
|
US 20150035359 A1 |
Feb 5, 2015 |
|
Foreign Application Priority Data
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Jul 30, 2013 [KR] |
|
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10-2013-0090288 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02J
3/32 (20130101); H02J 9/062 (20130101); H02J
3/00 (20130101); H02J 2310/12 (20200101); Y02B
70/30 (20130101); Y04S 20/20 (20130101) |
Current International
Class: |
H02J
3/00 (20060101); H02J 3/32 (20060101); H02J
9/06 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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WO 2010089607 |
|
Aug 2010 |
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GB |
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WO 2013095478 |
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Jun 2013 |
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IE |
|
1020080054259 |
|
Apr 2009 |
|
KR |
|
1020110074941 |
|
Jun 2013 |
|
KR |
|
Primary Examiner: Barnie; Rexford
Assistant Examiner: Chowdhuri; Swarna N
Attorney, Agent or Firm: Stevens; David R. Stevens Law
Group
Claims
What is claimed is:
1. An energy storage system included in an Uninterruptible Power
Supply (UPS) for supplying a power source to a load that needs the
uninterruptible power, comprising: a commercial power source unit
configured to supply a first power source to the load; a battery
configured to supply a second power source to the load; a power
failure monitoring unit configured to monitor a power failure state
in the commercial power source unit; a charging/discharging
determination unit configured to determine a charging state of the
battery and to estimate remaining capacity of the battery; a power
source control unit configured to control the commercial power
source unit and the battery in response to output of the power
failure monitoring unit or the charging/discharging determination
unit so that the first power source or the second power source is
supplied to the load; and an operation time setting unit configured
to set a peak time zone of the load; wherein the power source
control unit, when the first power source is normal and it is the
peak time zone, divides and supplies the first power source and the
second power source to the load, while the second power source is
supplied within an available remaining battery capacity except for
an essential remaining capacity of a battery that needs to be
essentially maintained in emergency; wherein the power source
control unit, when the first power source is normal and when it is
not the peak time zone, controls the first power source to be
supplied to the load; wherein the power source control unit, when
the first power source is cut off, controls the second power source
to be supplied to the load; wherein the power source control unit
determines whether it is possible to supply only the available
remaining battery capacity to the load during the peak time zone;
wherein when it is impossible to supply only the available
remaining battery capacity to the load, the power source control
unit calculates a current capacity that may continue to be
discharged at a substantially constant rate during the peak time
using only the available remaining battery capacity and supplies
the calculated current capacity to the second power source during
the peak time zone such that the second power source is shared with
the first power source to be supplied to the load.
2. The energy storage system of claim 1, wherein the power source
control unit shares and supplies the first power source and the
second power source, while calculating the remaining capacity of
the battery and a load current periodically and changing the second
power source into a suppliable current.
3. The energy storage system of claim 1, wherein: the UPS comprises
a first UPS and a second UPS, the first UPS and the second UPS
operate alternately, and the battery of the second UPS is charged
when the battery of the first UPS is discharged.
4. The energy storage system of claim 1, wherein: the UPS comprises
a first UPS and a second UPS, and the first UPS and the second UPS
are driven simultaneously and charged simultaneously.
5. The energy storage system of claim 1, further comprising: a
display unit configured to display a state of the battery, and an
alarm unit configured to output a warning sound or an emergency
lamp in response to a state displayed on the display unit.
6. A method of operating an Uninterruptible Power Supply (UPS)
comprising an energy storage system for supplying a power source to
a load that needs the uninterruptible power, the method comprising
steps of: (a) monitoring, by a power failure monitoring unit, a
power failure state of a commercial power source unit for supplying
a first power source to the load and determining, by a
charging/discharging determination unit, a charging state of a
battery for supplying a second power source to the load; (b)
setting, by an operation time setting unit, a peak time zone of the
load; (c) dividing, by a power source control unit, the first power
source and the second power source in the peak time zone set at the
step (b) and supplying the first power source and the second power
source to the load when the first power source is normal; and (d)
controlling, by the power source control unit, the first power
source to be supplied to the load when the power source is normal
and it is not the peak time zone and the second power source to be
supplied to the load when the first power source is at the power
failure state; wherein, in the step (c), the charging/discharging
determination unit calculates a remaining capacity of a battery and
the power source control unit supplies the second power source
within an available remaining battery capacity except for an
essential remaining capacity of the battery that needs to be
essentially maintained in emergency; wherein, in the step (c), the
power source control unit determines whether only the available
remaining battery capacity may be supplied to the load during the
peak time zone, and when it is impossible to supply only the
available remaining battery capacity to the load, the power source
control unit calculates a current capacity that may continue to be
discharged at a substantially constant rate during the peak time
using only the available remaining battery capacity and supplies
the calculated current capacity to the second power source during
the peak time zone such that the second power source is shared with
the first power source to be supplied to the load.
7. The method of claim 6, wherein in the step (c), the power source
control unit calculates the remaining capacity of the battery and a
load current periodically during the supplying of the first power
source and the second power source and changes the second power
source into a suppliable current.
8. The method of claim 6, wherein the step (a) comprises displaying
or notifying the state of the commercial power source unit and the
operating state of the battery determined by the power failure
monitoring unit and the charging/discharging determination
unit.
9. The method of claim 6, wherein the steps (a) to (c) are
repeatedly executed by a first UPS and a second UPS.
10. The method of claim 6, wherein the steps (a) to (c) are
simultaneously performed by a first UPS and a second UPS.
Description
CROSS REFERENCE TO RELATED APPLICATION
The present application claims the benefit of Korean Patent
Application No. 10-2013-0090288 filed in the Korean Intellectual
Property Office on Jul. 30, 2013, the entire contents of which are
incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to the energy storage system of an
Uninterruptible Power Supply (UPS) equipped with the battery and a
method of driving the same and, more particularly, to the energy
storage system of a UPS equipped with the battery, wherein some
capacity of the battery is used as an energy source by controlling
the discharge power of the battery using a rectifier and a
bidirectional converter used in the UPS, thereby being capable of
reducing the consumption power of a user and using the remaining
capacity as reserved power in emergency, and a method of driving
the same.
2. Description of the Related Art
Recently, an energy storage system (ESS) that may be said to be the
core of a smart grid is a system for storing energy. Various
devices for storing energy have been developed. A representative
storage device is for storing energy in the battery through a
charger during night time for which a power demand is small and for
discharging the stored energy through a discharger during time for
which a power demand is great. This is commonly called a system
association type energy storage system.
In order to store energy, a converter for converging AC into DC and
an inverter for converting DC into Ac are basically required. In
this case, if a product using DC as an energy source, such as the
battery and a super capacitor, is used, an AC/DC conversion
converter or a bidirectional converter having a
charging/discharging function is also required. An UPS may
basically perform AC/DC conversion and DC/AC conversion under the
control of a controller and the charging/discharging function using
a converter. Furthermore, an additional system for additional
system association is required.
The UPS also has a function that is prepared for a case where an
uninterruptible device is unable to perform a normal function owing
to the failure of elements that form the UPS, such as the power
converter and the battery, that is, an energy storage device.
In order to increase the use of an energy storage system based on a
physical energy change or chemical energy conversion, lost of
efforts have been made in a politic way. More particularly, lots of
efforts are being made to development energy storage system
technology for the supply of power consecutively, that is,
continuously.
The battery has a factor in the reduction of the lifespan according
to the number of times of charging and discharging depending on the
type of battery. A lead battery is problematic in terms of
inspection and management, such as ineffective handling in
emergency, because the activation of a chemical substance that
forms the battery, the terminal voltage irregularity of the
battery, and a change in the generation of corrosion of the
terminal unit are not checked. For this reason, a lithium battery
further has a function called the battery management system (BMS)
in order to prevent the problems and damage attributable to
overcharging.
In particular, recently, a reduction of power attributable to the
shortage of supply in the peak load of a commercial power source is
emphasized. From a viewpoint of power demand management and owing
to a difference in a billing system according to each time zone,
there is a social and economical need, such as the operation of an
emergency generator in order for consumers to manage demands, such
as power bill management.
In such a reality, in general, the battery of a UPS owned by a
power consumer has a capacity capable of stably supplying power
required by the consumer for a specific time that is determined by
the consumer, but this is only used when a power failure occurs in
a commercial power source. That is, the existing UPS using the
battery performs a discharging operation using power of the battery
only in the state in which a power failure has occurred in an input
power source. Although a momentary power failure occurs, a UPS is
inevitably used in a computer server and production equipment that
require a lot of time taken for recovery in order to prepare for
the momentary power failure.
Examples of technology for solving the problem are disclosed in
Patent Documents 1 and 2.
For example, Patent Document 1 discloses a method of estimating the
remaining capacity of the battery, including steps of checking
whether or not the battery is in the first connection state,
checking whether the battery is in a discharging state or a
charging state if, as a result of the check, the battery is found
to be in the connection state, measuring voltage of the battery if,
as a result of the check, the battery is found to be in discharging
state, determining whether or not the battery has been stabilized
by comparing the voltage of the battery with a predetermined
stabilization determination voltage, calculating a voltage drop by
calculating the amount of discharged current, calculating an open
circuit voltage using the calculated voltage drop voltage and the
measured voltage, calculating an initial remaining capacity
corresponding to the calculated open circuit voltage, calculating
the final remaining capacity using the initial remaining capacity
and a predetermined diequilibration efficiency.
Furthermore, Patent Document 2 discloses an apparatus for
diagnosing an aging state and a diagnostic method using the same,
wherein an ESR value or a loss angle value tan .delta. are measured
by flowing a measurement current signal into the electrolytic
capacitor of the DC booth of a power conversion device, the
malfunction or damage of the power conversion device is diagnosed
based on the measured ESR value or loss angle value, characteristic
data, such as internal resistance of each battery to be measured,
is measured so that the aging state of the battery system that is
an essential element of a UPS can be measured and monitored at the
same time, and a complex abnormal state according to the aging or
deterioration of the power conversion device is previously
monitored diagnosed based on the measured characteristic data.
However, the aforementioned prior arts do not disclose technology
in which the battery is used as energy more efficiently in a UPS
basically including a rectifier (or a converter), a
charging/discharging unit (or a bidirectional converter), an
inverter, a bypass, a control board, and the battery.
PRIOR ART DOCUMENT
Patent Document
(Patent Document 1) Korean Patent No. 10-1261149 (issued on Apr.
29, 2013)
(Patent Document 2) Korean Patent No. 10-0998577 (issued on Nov.
30, 2010)
SUMMARY OF THE INVENTION
Accordingly, the present invention has been made keeping in mind
the above problems occurring in the prior art, and an object of the
present invention is to provide the energy storage system of a UPS
equipped with the battery and a method of driving the same, which
are capable of reducing power consumption by reusing energy using
the battery, that is, an energy source, more economically,
providing a user with profit resulting from the power consumption,
and improving productivity to a maximum extent while providing
power to the user.
Another object of the present invention is to provide the energy
storage system of a UPS equipped with the battery and a method of
driving the same, which are capable of increasing the discharging
efficiency of the battery by controlling discharging power so that
a specific amount of the battery capacity is not rapidly
discharged.
Further another object of the present invention is to provide the
energy storage system of a UPS equipped with the battery and a
method of driving the same, which are capable of effectively
handling demand management and power bill management even when a
commercial power source is normally supplied.
Yet another object of the present invention is to provide the
energy storage system of a UPS equipped with the battery and a
method of driving the same, which are capable of supplying
stabilized power to a load although an energy storage operation is
performed in accordance with a problem, such as a DC link
overvoltage alarm attributable to a rise of DC link voltage due to
the influence of a bidirectional converter.
In accordance with an aspect of the present invention, an energy
storage system included in an UPS includes a commercial power
source unit configured to supply a first power source to a load,
the battery configured to supply a second power source to the load,
a power failure monitoring unit configured to monitor a power
failure state in the commercial power source unit, a
charging/discharging determination unit configured to determine a
charging state of the battery, and a power source control unit
configured to control the commercial power source unit and the
battery in response to output of the power failure monitoring unit
or the charging/discharging determination unit so that the first
power source or the second power source is supplied to the
load.
The energy storage system in accordance with an embodiment of the
present invention further includes an operation time setting unit
configured to set an operation time of the load, wherein the power
source control unit performs control based on the operation time
set by the operation time setting unit so that the first power
source and the second power source are supplied to the load.
In the energy storage system in accordance with an embodiment of
the present invention, the power source control unit performs
control in response to the charging state of the battery determined
by the charging/discharging determination unit so that the first
power source is supplied to the battery and performs control in
response to the power failure state monitored by the power failure
monitoring unit so that the first power source and the second power
source are supplied to the load.
In the energy storage system in accordance with an embodiment of
the present invention, the UPS includes a first UPS and a second
UPS, the first UPS and the second UPS operate alternately, and the
battery of the second UPS is charged when the battery of the first
UPS is discharged.
In the energy storage system in accordance with an embodiment of
the present invention, the UPS includes a first UPS and a second
UPS, and the first UPS and the second UPS are driven simultaneously
and charged simultaneously.
The energy storage system in accordance with an embodiment of the
present invention further includes a display unit configured to
display a state of the battery and an alarm unit configured to
output a warning sound or an emergency lamp in response to a state
displayed on the display unit.
In accordance with an aspect of the present invention, a method of
operating a UPS including an energy storage system includes steps
of (a) determining, by a power failure monitoring unit and a
charging/discharging determination unit, a state of a commercial
power source unit and a charging state of the battery for supplying
a first power source and a second power source to a load, (b)
setting, by an operation time setting unit, a peak time zone of the
load, and (c) dividing, by a power source control unit, the first
power source and the second power source in the peak time zone set
at the step (b) and supplying the first power source and the second
power source to the load.
In the method of driving the UPS in accordance with an embodiment
of the present invention, the step (c) includes calculating, by the
charging/discharging determination unit, a remaining capacity of
the battery and performing, by the power source control unit,
control so that the supply of the second power source is executed
outside an essential remaining capacity of the battery that needs
to be essentially maintained in emergency.
In the method of driving the UPS in accordance with an embodiment
of the present invention, the step (c) includes supplying, by the
power source control unit, the second power source periodically
according to a capacity of the battery determined by the
charging/discharging determination unit.
In the method of driving the UPS in accordance with an embodiment
of the present invention, the step (a) includes displaying or
notifying the state of the commercial power source unit and the
operating state of the battery determined by the power failure
monitoring unit and the charging/discharging determination
unit.
In the method of driving the UPS in accordance with an embodiment
of the present invention, the steps (a) to (c) are repeatedly
executed by a first UPS and a second UPS.
In the method of driving the UPS in accordance with an embodiment
of the present invention, the steps (a) to (c) are simultaneously
performed by a first UPS and a second UPS.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an exemplary diagram of the energy storage system of
uninterruptible power supplies equipped with batteries in
accordance with an embodiment of the present invention;
FIG. 2 is a block diagram showing the construction of a main
control board shown in FIG. 1;
FIGS. 3A, 3B, 3C and 3D are diagrams illustrating various types of
operation modes of the UPS equipped with the battery in accordance
with an embodiment of the present invention;
FIG. 4 is a block diagram of a bidirectional converter controller
for the UPS for handling an excessive response;
FIGS. 5A and 5B are graphs showing the test results of an excessive
response;
FIG. 6 is a block diagram of the controller for sharing a
commercial power source battery load;
FIG. 7 is a flowchart illustrating the energy storage method of the
UPS equipped with the battery in accordance with an embodiment of
the present invention; and
FIG. 8 is a flowchart illustrating common operation mode in
accordance with an embodiment of the present invention.
DETAILED DESCRIPTION
The above objects, other objects, and new characteristics of the
present invention will become more apparent by technology disclosed
in the specification and the accompanying drawings.
First, a relationship between a UPS to which the present invention
is applied and the battery included in the UPS is described
below.
The battery capacity of the UPS is determined according to the
setting of a maximum discharging time.
The discharging current of a UPS for single phase and 3-phase
output is identically calculated and determined by a UPS capacity
and the battery use voltage. A discharging current Id is calculated
as in Equation 1 based on a UPS of 100 KVA.
.times..times..times..times..times..times..times..times..times..times..ti-
mes..times..times..times..times..times..times..times..times..times..times.-
.times..times..times..times. ##EQU00001##
In Equation 1, assuming that the power failure compensation time of
the UPS is 30 minutes and a lead battery is used according to
Equation 1, a use capacity is a 2 V 250 AH 240 cells according to
the specification of the battery manufacturer at a final voltage of
1.75 V. In this case, assuming that the power failure compensation
time is 1 hour, the use capacity is a 2 V 400 AH 240 cells
according to the specification of the battery manufacturer.
For example, if 30% of a total battery capacity is used in an
energy storage operation and the remaining 70% thereof is used as
emergency power for a power failure, Equation 2 is obtained.
.times..times..times..times..times..times. ##EQU00002##
In Equation 2, if the energy storage operation is set to 2 hours,
Equation 3 is obtained.
.times..times..times..times..times..times..times..times.
##EQU00003## .times..times..times..times..times..times..times.
##EQU00003.2##
In Equation 3, 0.74 is battery 2-hour discharging efficiency 74%.
If the battery is discharged for 3 hours, discharging efficiency is
increased to 84%. That is, as the discharging time is increased,
discharging efficiency becomes better. The discharging efficiency
may be slightly different depending on the raw materials and
manufacturer of the battery.
For the energy storage operation of the battery for 2 hours, a
required current is 27.7 A per hour according to Equation 3.
The capacity of the UPS and the voltage condition of the battery
may be different depending on a user, but most of users use loads
less than 50% of an equipment capacity.
If a user uses a load of 50 KW,
.times..times..times..times..times..times. ##EQU00004##
As described above, DC power of 124 A is required. Power required
for the rectifier is calculated as in Equation 5 based on 124 A.
124 A-27.7 A=96.3 A (5)
Power for the energy storage operation is calculated as in Equation
6 according to the above equations. 27.8
A.times.1.75.times.240=11.68 KW/H (6)
If a user who has used the battery having the 30-minute power
failure compensation time in the UPS capacity of 100 KVA uses a
load of 50 KW/H, power reduced by the energy storage operation can
be obtained as in Equation 6.
That is, the user can increase the utilization of the battery and
secure emergency power for a power failure through the energy
storage operation, recover some of an installation cost to the use
of the battery through such a reduction of energy, and increase a
power reservation ratio of power used through reduced power use
during daytime.
Furthermore, if the battery capacity is increased in order to
increase a power failure compensation time, power can be reduced
more. The lifespan of the battery can be extended by reducing the
number of times of discharging related to the lifespan.
As described above, the technology of the battery continues to be
developed and the utilization of raw materials continues to be
increased.
However, the lifespan of a lead battery for floating charging that
is used in a UPS is expected to be 3 to 5 years. This may vary
depending on recommended battery use temperature conditions (e.g.,
20.about.25.degree. C.). That is, if the lead battery for floating
charging is used for 3 years using only a power failure
compensation function, a cell failure in which the function of the
battery is lost starts to occur and thus the battery becomes the
subject of disuse.
The technology of the battery is developed, and the technology of a
UPS is also developed. If technology in accordance with an
embodiment of the present invention is grafted, it is expected that
energy may be used more efficiently.
First, an important function of the UPS is to continue to supply a
power source to a load when an input power source is subject to a
power failure. If a power failure occurs in the input power source
during the battery discharging operation, a discharging operation
continues to be performed. If a power failure occurs in an input
power source during the battery charging operation, a power source
continues to be supplied to a load through a normal discharging
operation. If the input power source is recovered, an energy
storage operation is performed the battery is charged by
determining the remaining battery capacity.
If the UPS performs a normal operation by the inverter during the
energy storage operation, a power source continues to be supplied
to the load in any case. If the inverter fails, the power source is
supplied to the load through the bypass.
Second, in the parallel operation of uninterruptible power
supplies, an energy storage operation is performed like in a single
operation, but an additional advantage is that the uninterruptible
power supplies alternately perform their discharging operations.
That is, when one of the uninterruptible power supplies starts a
discharging operation, the other of the uninterruptible power
supplies performs a normal operation. When one of the
uninterruptible power supplies finishes the discharging operation,
it starts a charging operation and the other of the uninterruptible
power supplies starts a discharging operation.
A user who uses a major load uses a lot of uninterruptible power
supplies in parallel. In such a case, if the uninterruptible power
supplies perform discharging operations one by one, an energy
storage operation can be performed for a longer time. Accordingly,
the time taken to charge the battery after the battery is
discharged during daytime can be greater than the time when a
single UPS is used, discharging efficiency of the battery can be
increased, and the lifespan of the battery can be extended.
Furthermore, if the UPS repeatedly performs the energy storage
operation during daytime, the battery is inevitably charged during
daytime. A charging method for minimizing consumption power during
the charging time needs to be taken into consideration.
Furthermore, the design needs to be reviewed and performed
according to a method recommended by the battery manufacturer, and
the reuse of the raw materials of the battery having expired
lifespan also needs to be taken into consideration.
In a UPS using the battery in accordance with an embodiment of the
present invention, a main control board controls a rectifier and a
charger/discharger for an energy storage operation.
In order to control the charger/discharger, the main control board
sets an energy storage operation and operation start time.
For the energy storage operation, the UPS using the battery
executes the setting of the battery capacity based on a power
failure compensation time in response to a request from a user.
Furthermore, the battery applied to the present invention includes
deep cycle service.
When the battery capacity is set, a discharging capacity is set by
taking the depth of discharge (% DOD) of the battery into
consideration. As the discharging capacity is increased, the
charging/discharging cycle of the battery is reduced and thus the
lifespan of the battery is reduced. For this reason, for example,
the design may be performed so that only 30% of a total battery
capacity is used in a discharging operation and the remaining 70%
thereof is used as emergency power for the lifespan of the battery
and a power failure.
The battery capacity according to a power failure compensation time
is determined by the capacity of a UPS, efficiency of an inverter,
the final voltage of the battery, and the number of batteries. In
this case, the battery capacity is selected as a calculated current
based on battery data.
The battery capacity of a UPS is selected based on a load of 100%,
but a recommended load amount is 50%. Most of users use 50% or less
of the capacity of a UPS. That is, a power failure compensation
time may be more increased than that requested by a user depending
on the use of a load.
For the energy storage operation, the main control board sets an
energy storage operation time, the start time and the end time, the
battery capacity, the final voltage of the battery, the number of
batteries, the battery type, and the battery discharging capacity.
The energy storage operation time is divided into the morning and
the afternoon, that is, power peak time zones.
When the UPS is in a normal operating state, that is, when the UPS
supplies a load to the inverter, the main control board calculates
the battery discharging current for the energy storage operation
based on a corresponding value.
In this case, when the energy storage operation time is checked,
the main control board changes the charger into the discharger and
increases the amount of discharging based on a current limit
controlled by the bidirectional converter. The discharger performs
discharging up to the battery discharging capacity limit, and the
remaining power is supplied to the load through the rectifier.
Furthermore, like in the discharging characteristic of the battery,
when the battery is discharged, the UPS performs an energy storage
operation. When the discharging characteristic of the battery
deviates, the UPS informs a user of an alarm state by outputting
the battery abnormality alarm through a display window and the
output. A loss attributable to a power failure can be minimized by
such the battery check. The start and end of the discharging
operation are also delivered to a user using a message so that the
user can check the state of the UPS.
The battery has better discharging efficiency as the discharging
time is increased. The main control board is configured by taking
such better discharging efficiency into consideration.
When an end time set in the main control board is reached, the
current limit of the bidirectional converter is released and thus
the discharger switches to charger mode and charges the battery.
Furthermore, when a discharging time set in the main control board
is reached, the above operation is repeated. The above operation is
repeatedly performed during daytime for which power consumption is
great and charging is performed during time for which power
consumption is small, thereby minimizing power consumption.
Furthermore, discharging voltage of the battery needs to be set by
taking the depth of discharge (% DOD) of the battery into
consideration. The lifespan of the battery is determined by the
depth of discharge. In order to maximize the lifespan of the
battery and the utilization of the battery by a user, the battery
manufacturer sets the discharging voltage of the battery by taking
the depth of discharge into consideration into consideration.
Furthermore, in order to prepare for a possible power failure for a
long time or a possible power failure attributable to the failure
of power system equipment on the user side, the design is performed
so that the battery is discharged up to a specific voltage and the
remaining voltage is prepared for the power failures.
The battery that may be used in the present invention may be made
of lead (Pb), nickel (Ni), and lithium (Li) as raw and major
materials and has the depth of discharge (% DOD).
The construction of the present invention is described below with
reference to the accompanying drawings.
FIG. 1 is an exemplary diagram of the energy storage system of
uninterruptible power supplies equipped with batteries in
accordance with an embodiment of the present invention.
As shown in FIG. 1, the UPS equipped with the battery in accordance
with an embodiment of the present invention includes a first UPS
and a second UPS. The first UPS and the second UPS alternately
operate. A construction in which when the battery of the first UPS
is discharged, the battery of the second UPS is charged may be
adopted. Furthermore, a construction in which the first UPS and the
second UPS are discharged at the same time may be adopted.
Furthermore, elements shown in FIG. 1 correspond to a UPS that is
commonly used in the field of the present invention and include a
rectifier configured to receive and rectify a commercial power
source AC INPUT, an inverter configured to convert the rectified DC
into AC, a bidirectional DC-DC converter configured to charge a
power storage device (hereinafter referred to as a `battery`) in
order to charge the battery capable of charging/discharging the DC
power rectified by the rectifier or supply the inverter with power
charged into the battery, and a main control board.
The main control board includes a digital signal processor (DSP)
and a field-programmable gate array (FPGA). The main control board
controls the rectifier, the inverter, and the bidirectional DC-DC
converter depending on the power supply state and conditions set by
a user and also controls the general operation of the UPS, such as
displaying operation conditions, an operating state, and a power
supply state or receiving input from a user.
In the present invention, as shown in FIG. 1, the first UPS and the
second UPS are provided, and a bypass line is further configured to
supply a commercial power source to a load if the UPS does not
operate due to a failure in the rectifier, the inverter, etc. The
construction and operating principle of the bypass line are known
in the art, and thus a detailed description thereof is omitted.
Furthermore, the elements of each of the first UPS and the second
UPS shown in FIG. 1 include a rectifier, an inverter, and a
bidirectional DC-DC converter for supplying power to the battery,
supplementing insufficient voltage supplied by a commercial power
source or electric generator, and supplying power when a power
failure occurs, as disclosed in technology commonly used or known
in the technical field of the present invention, for example, in
Korean Patent No. 10-1211114 or 10-1247282. Accordingly, a detailed
description of the known art is omitted.
For example, the power conversion semiconductor element of each of
the rectifier, the inverter, the charger/discharger, and the bypass
may be formed of any one of an Insulated Gate Bipolar Transistor
(IGBT), a Silicon Controlled Rectifier (SCR), a Gate Turn-Off (GTO)
transistor, and a Bipolar Junction Transistor (BJT). In particular,
the rectifier may be configured to have a charger/discharger
function, and the rectifier and the charger/discharger may be
separately configured and driven. The rectifier or the
charger/discharger may be formed of a switching element having a
discharging current capacity suitable for the capacity of the UPS
using one of an Insulated Gate Bipolar Transistor (IGBT), a Gate
Turn-Off (GTO) transistor, and a Bipolar Junction Transistor (BJT)
that enable high-speed switching so that the rectifier or the
charger/discharger functions as an accurate and fast switch.
The main control board of FIG. 1 and various types of operation
mode of the main control board are described below with reference
to FIGS. 2 and 3.
FIG. 2 is a block diagram showing the construction of the main
control board shown in FIG. 1, and FIG. 3 is a diagram illustrating
various types of operation modes of the UPS equipped with the
battery in accordance with an embodiment of the present
invention.
As shown in FIG. 2, the energy storage system in accordance with an
embodiment of the present invention is an energy storage system 100
included in each of the first UPS and the second UPS. The energy
storage system 100 includes a commercial power source unit 20
configured to supply a load 10 with a first power source, the
battery 30 configured to supply the load 10 with a second power
source, and a main control board 40 configured to control a power
source supplied to the load 10 depending on the state of the
commercial power source unit 20 and the battery 30.
The energy storage system 100 in accordance with an embodiment of
the present invention further includes a display unit 50 configured
to display the state of the battery 30, for example, the battery
abnormality alarm when a discharging characteristic provided by the
battery manufacturer deviates and an alarm unit 60 configured to
notify a user of the state of the energy storage system 100 by
outputting voice, such as a warning sound, for example, a `battery
power failure mode operation` or a `power failure state` or
outputting an emergence lamp, for example, the flickering of a red
light depending on a state displayed on the display unit 50.
The main control board 40 includes a power failure monitoring unit
41 configured to monitor a power failure state in the commercial
power source unit 20, a charging/discharging determination unit 42
configured to determine the charging state of the battery 30, and a
power source control unit 43 configured to control the commercial
power source unit 20 and the battery 30 so that the first power
source or the second power source is supplied to the load 10
depending on the output of the power failure monitoring unit 41 or
the charging/discharging determination unit 42.
The main control board 40 further includes an operation time
setting unit 44 configured to set an energy storage operation time
in the load 10. The power source control unit 43 performs control
so that the first power source and the second power source are
supplied to the load in accordance with an operation time set in
the operation time setting unit 44.
The main control board 40 includes a microprocessor configured to
have the calculation ability and a memory device configured to
store the condition states. The power failure monitoring unit 41,
the charging/discharging determination unit 42, the power source
control unit 43, and the operation time setting unit may be
implemented in such a manner that the microprocessor operates and
controls a program stored in the memory device.
Furthermore, the power source control unit 43 performs control so
that the first power source is supplied to the battery 30 depending
on the charging state of the battery in the charging/discharging
determination unit 42 and performs control so that the second power
source is supplied to the load 10 depending on the charging state
of the battery in the power failure monitoring unit 41.
That is, as shown in FIG. 3A (a thick line indicates a power flow),
in the case of normal operation mode, that is, a common operating
state, the power source control unit 43 of the main control board
40 performs control so that power is supplied to the load 10
through the commercial power source unit 20 and the battery 30 is
charged. That is, normal operation mode is the state in which power
is operated as in a power flow (indicated by the thick line) in a
consumer that uses the UPS system. In such a state, the power
source control unit 43 performs control so that a first power
source (i.e., a commercial power source) is supplied to the load 10
and the battery 30 is charged.
When the charging of the battery 30 is completed, that is, if it is
determined that the battery 30 does not need to be charged based on
a determination of the charging state in the charging/discharging
determination unit 42, as shown in FIG. 3B (a thick line indicates
a power flow), the power source control unit 43 stops the charging
operation of the bidirectional DC-DC converter and performs control
so that the first power source is supplied to the load 10. That is,
the power source control unit 43 performs commercial power
source-single operation mode.
In contrast, if the power failure monitoring unit determines that
input to the UPS is power failure operation mode, as shown in FIG.
3C (a thick line indicates a power flow), the power source control
unit 43 performs control so that only the second power source is
supplied to the load 10, and the alarm unit 60 indicates a `battery
power failure mode operation` that gives a warning. For example,
the alarm unit 60 may give a plurality of warnings according to a
user setting.
In accordance with the present invention, in sharing operation mode
in which the load 10 is shared by the first power source of the
commercial power source unit 20 and the second power source of the
battery 30, as shown in FIG. 3D (a thick line indicates a power
flow), the power source control unit 43 performs control so that
the load 10 is shared and supplied with the first power source and
the second power source during a peak time set by the operation
time setting unit 44.
Control of the rectifier, the converter, etc. shown in FIG. 1 is
described below with reference to FIGS. 4 to 6.
FIG. 4 is a block diagram of the controller of the bidirectional
converter for the UPS for handling an excessive response, FIG. 5 is
a graph showing the test results of the excessive response, and
FIG. 6 is a block diagram of a controller for sharing a commercial
power source battery load.
In order to increase an excessive response according to a change of
the load, the UPS requires DC link voltage converted by the
bidirectional converter and a current controller. In the present
invention, a bidirectional converter controller, such as that shown
in FIG. 4, is provided.
The bidirectional converter controller of FIG. 4 is described below
with reference to FIG. 5. Referring to FIG. 5A, the results of
tests according to a change of the load when the bidirectional
converter performs a discharging operation show that DC link
voltage is shifted when the load is turned on or off. In such a
case, the UPS generates a DC overvoltage alarm in actual
situations. FIG. 5B shows that a change of the DC link voltage is
reduced through control of a gain value by the bidirectional
converter controller. As in the tests, a change of the load can be
handled using voltage using the voltage and the current controller
of the bidirectional converter. Furthermore, there is a need for
the current controller capable of controlling power supplied to the
battery 30 for an energy storage operation. When a load is changed,
DC link voltage may be increased by the controller. Thus, if the
controller controls a rise of DC link voltage by controlling a gain
value, an energy storage operation can be performed so that a
commercial power source battery load is shared.
That is, in the UPS applied to the present invention, test
conditions of an excessive response are present. In the test
conditions, when the UPS normally operates, the battery is
connected and the time taken for output voltage to be recovered is
measured by changing a load. For tests for an excessive response,
reference may be made to KS C IEC 62040-3 5.3 term. Korean
industrial Standards (KS) describe the test method, but the
resulting values are widely set to 10%. Such an excessive response
is determined by the specification of a manufacturer. The test
standard of the UPS in accordance with an embodiment of the present
invention is within .+-.5% when a load suddenly changes by 50% and
a response thereof is within 50 msec. In this case, the
bidirectional converter may be influenced by a change of the load
as shown in FIG. 5, which may result in a DC link overvoltage alarm
attributable to a rise of DC link voltage. In order to prevent such
a problem, a stabilized power source may be supplied to the load
even when an energy storage operation is performed.
The controller for sharing the battery load is described below with
reference to FIG. 6.
In FIG. 6, a value calculated by the main control board 40 based on
a capacity related to a load amount, a discharging peak time zone,
and the battery and battery discharging efficiency according to a
discharging capacity, a final voltage, a discharging voltage, and a
discharging time determines the battery discharging current
value.
The battery discharging current value is
I.sub.BAT(x).sub._.sub.ref. The value is controlled based on the
reference value of the battery discharging current. A required
rectifier reference current value according to an initial load
amount in an energy storage operation and the battery discharging
current is I.sub.CON.sub._.sub.IN.
In this case, when a load is changed, the main control board 40
calculates a changed value I.sub.Diff.sub._.sub.ref and controls
the value I.sub.CON.sub._.sub.ref of the rectifier using the
rectifier current limit function of the UPS.
As described above, the main control board 40 prepares for a change
of the load and a power failure through continuous calculation.
Secondarily, the UPS controls the current of the bidirectional
converter in discharging (i.e., boost mode) based on the calculated
value and controls a rise of DC link voltage corresponding to a
change of the load by controlling the DC link voltage in response
to a changed voltage of the battery so that the battery discharging
operation, that is, an energy storage operation, is performed in a
predetermined peak time zone.
A method of driving the UPS in accordance with an embodiment of the
present invention is described with reference to FIG. 7.
FIG. 7 is a flowchart illustrating the operation method of the UPS
equipped with the battery in accordance with an embodiment of the
present invention, and FIG. 8 is a flowchart illustrating common
operation mode in accordance with an embodiment of the present
invention.
First, power is supplied to the load through the first power source
of the commercial power source unit 20 in common operation state,
and a power flow in a consumer who uses the UPS system in a normal
operating state, that is, a state in which the battery 30 is
charged, is shown in FIG. 3A. In this state, the first power source
is supplied to the load 10 and the battery 30 is charged.
The power failure monitoring unit 41 of the main control board 40
determines whether or not the first power source is normal. Such a
determination may be made by diagnosing whether or not a rectifier,
an inverter, a bidirectional DC-DC converter, and the battery
described in technology that is commonly used and known in the
technical field of the present invention, for example, in Korean
Patent No. 10-1211114 or 10-1247282 at step S10. The
charging/discharging determination unit 42 determines the battery
charging state in order to determine whether or not the battery 30
needs to be charged by detecting terminal voltage of the battery 30
using the battery terminal voltage measurement technique disclosed
in Korean Patent No. 10-0386053 or 10-0989178, at step S20.
If, as a result of the determination, it is determined that the
battery 30 needs to be charged at step S30, the power source
control unit 43 of the main control board 40 drives the
bidirectional DC-DC converter in charging mode so that the battery
30 is charged and at the same time, power is supplied to the load
10. Accordingly, as shown in FIG. 3A, the battery 30 is charged by
supplying the first power source, that is, a commercial power
source, to the load 10 and the battery 30 at step S40.
If, as a result of the determination, it is determined that the
battery 30 does not need to be charged at step S30, the charging
operation of the bidirectional DC-DC converter is stopped and power
source operation mode is performed at step S50, as shown in FIG. 3B
or 3D. Power source operation mode at step S50 includes single
operation mode by the commercial power source unit 20 and common
operation mode by the commercial power source unit 20 and the
battery 30. Single operation mode and common operation mode are
described later with reference to FIG. 8.
Thereafter, the power failure monitoring unit 41 determines whether
or not the commercial power source, that is, the first power
source, is normally supplied using a voltage sensor that is a known
art at step S60. If, as a result of the determination at step S60,
it is determined that the commercial power source, that is, the
first power source, is not normally supplied, that is, in the case
of a power failure state as shown in FIG. 3C, the power source
control unit 43 drives the bidirectional DC-DC converter so that
power of the battery, that is, the second power source, is supplied
to the load 10 through the battery 30 at step S70. In such
technology, as known and commonly used in Korean Patent No.
10-0386053 or 10-0989178, for example, the remaining capacity of
the battery is determined, the amount of power consumed by the load
10 and the remaining capacity of the battery are checked, and the
time for which power can be supplied is displayed. If, as a result
of the determination at step S60, it is determined that the
commercial power source, that is, the first power source, is
normally supplied, step S50 is performed.
When step S70 is executed by the power failure detection unit 41, a
signal of, for example `battery power failure mode operation` is
output through the alarm unit 60.
`Commercial power source battery load sharing operation mode` at
step S50 in which both the commercial power source unit 20 and the
battery 30 supply power sources to the load 10 is described in
detail below with reference to FIG. 8.
If the power failure monitoring unit 41 and the
charging/discharging determination unit 42 determine that the
battery does not need to be charged, the commercial power source is
normal, and there is no abnormality as a result of self-diagnosis
at step S50, the power source control unit 43 determines whether or
not a time zone is a power peak time zone input or set by the user
of the UPS in relation to the load 10 of a consumer through the
operation time setting unit 44 at step S51.
If, as a result of the determination, it is determined that the
time zone is the set or input power peak time zone of the load 10
at step S52, the charging/discharging determination unit 42
calculates the remaining battery capacity of the battery 30 at step
S53.
At step S53, the charging/discharging determination unit 42
calculates a current load current and the remaining battery
capacity and receives the range of the `essential remaining
capacity of the battery` that has been input by a user depending on
the conditions of load equipment or has been previously set and
that needs to be essentially maintained in emergency. If it is
determined that the current load current may be supplied using an
`available remaining battery processing capacity` other than the
set remaining battery capacity (e.g., 50% which may also be changed
by a user and randomly set for convenience of description assuming
that the capacity of consumer equipment that needs to be
essentially driven when a power failure occurs is 50%) during the
peak time (that may be set to about 2 hours and also changed by a
consumer or commercial power supply network operator), the `remnant
capacity peak power supply mode` is performed at step S54.
Calculation in remnant capacity peak power supply mode at step S54
is performed as follows. Such an example is only illustrative and
the present invention is not limited thereto.
For example, assuming that a UPS capacity is 100 KVA, a load
equipment capacity is 50 KW, battery rating voltage is 540 V, the
number of batteries corresponds to a 2V 240 cells, battery final
voltage is 1.75 V, and inverter power conversion efficiency is
0.96, the battery capacity is determined by the power failure
compensation time requirement of a user.
In the present invention, the power source control unit 43 controls
power of the battery 30 so that discharging is performed for 2
hours in relation to 30% when the peak time set by the operation
time setting unit 44 is 2 hours.
The following calculation shows another example under the
aforementioned conditions.
1) Calculation of a Maximum Discharging Current of 100 KVA
.times..times..times..times..times..times..times..times..times..times..ti-
mes..times..times..times..times..times..times..times..times..times..times.-
.times..times..times..times. ##EQU00005##
2) Selection of the Battery Capacity
If the power failure compensation time is 30 minutes, an electric
current required for the power failure compensation time of 30
minutes is 198 A because 200 AH is equal to a maximum of 173 A and
250 AH is equal to a maximum of 216 A based on lead battery data.
Since the 200 AH does not satisfy the specification, 2 V/250 AH/240
cells are selected according to the battery specification of the
battery manufacturer or a request from a user.
3) 30% of Battery Capacity in Energy Storage Operation 250
AH.times.0.3=75 AH
75 AH, that is, 30% of 250 AH, is used in the energy storage
operation, and the remaining 70% of 250 AH is used as emergency
power prepared for a power failure.
4) Discharging Time of 2 Hours (i.e., Peak Power Time) 75
AH/2H=37.5 A wherein 37.5 A.times.0.74 (battery discharging
efficiency is 74% during discharging for 2 hours)=27.7 A/H
The battery current for the energy storage operation requires 27.7
A per hours. If the discharging time is increased, the battery has
higher discharging efficiency (e.g., 84% during discharging for 3
hours). In such a case, 75 AH/3 H=25 A is required. That is, 21 A
is required per hour as in 25 A.times.0.84=21 A/H.
Accordingly, a total of DC power during operation for 2 hours=27.7
A.times.1.75 V (final voltage).times.240 (number of cells)=11.6
KW/H.times.2 H=23.2 KW.
A total of DC power during operation for 3 hours=21 A.times.1.75 V
(final voltage).times.240 (number of cells)=8.8 KW/H.times.3 H=26.4
KW.
If the energy storage operation time is increased as in the above
calculation, a lot of discharging power can be secured due to
improved discharging efficiency. Accordingly, energy can be reduced
that much.
5) when a Load Amount is 50 KW, Required DC Power is 124 A as in
the Following Calculation.
.times..times..times..times. ##EQU00006##
6) Required Load DC Power Load current=battery current+rectifier
current Rectifier current=load current-battery current 124 A-27.7
A=96.3 A: required rectifier current in a 2-hour energy storage
operation Rectifier current=load current-battery current 124 A-21
A=103 A: required rectifier current in a 3-hour energy storage
operation
That is, the battery of 27.7 A operates in the energy storage
operation, the rectifier supplies 96.3 A using the rectifier
current limit function, that is, the basic function of the UPS, and
a discharging operation is performed for the peak time set to 2
hours based on 124 A required for the load.
In order to improve discharging efficiency of the battery and also
perform the energy storage operation as described above, the
controller requires the battery current of the DC-DC converter.
70% of 250 AH, that is, 175 AH, in the calculation example of the
essential remaining battery capacity
30% of 250 AH, that is, 75 AH, in the calculation example of the
available remaining battery capacity
The charging/discharging determination unit 42 calculates the
current load current and the remaining battery capacity at step S53
and determines whether or not the current load current may be
supplied using the `available remaining battery capacity` other
than the `essential remaining capacity` during the current peak
time at step S55.
If, as a result of the determination at step S55, it is determined
that the current load current may not be supplied to the load 10
using the available remaining battery capacity during the current
peak time, the charging/discharging determination unit 42
calculates a current capacity that may continue to be discharged
during the peak time using only the `available remaining battery
capacity`.
As shown in FIG. 3D, `commercial power source battery load sharing
operation mode` in which discharging is performed using commercial
power discharged by only the current capacity calculated during the
peak time and the current capacity that may be continue to be
supplied by the battery during the peak time is performed at step
S56.
If, as a result of the determination at step S55, it is determined
that the current load current may not be supplied to the load 10
using the available remaining battery capacity during the current
peak time, battery charging mode is executed at step S57.
In this case, if the load current may not be supplied, the battery
load sharing ratio set by a user may be less than 1% of a total
load current, but this may be randomly set by a user.
Step S57 proceeds to step S20 in which the charging state of the
battery is determined.
At step S56, the power source control unit 43 calculates an
electric current that flows through the load 10 and the remaining
battery capacity in a specific cycle that is a specific cycle set
by a user, for example, a cycle calculated by the main control
board 40 by taking a process of calculating the capacity of the
battery and the characteristics of consumer equipment, determines
whether or not the calculated electric current and the remaining
battery capacity may continue to be supplied during the peak time,
and performs `cycle-based supply ability determination step` based
on a result of the determination at step S58.
If, as a result of the determination at step S58, it is determined
that the calculated electric current and the remaining battery
capacity may not be supplied during the peak time, the process
proceeds to step S57.
That is, in order to perform calculation as at step S58 according
to a change of the load and supply power to the load based on the
peak power time, the rectifier and the DC-DC converter are
controlled. In order to prevent the continued overdischarging of
the battery attributable to a reduced battery capacity due to the
use of the battery for a long time or the battery temperature,
voltage of the battery corresponding to an available remaining
battery capacity is set, the energy storage operation is stopped
based on any one of the set voltage and a peak time setting value
that is first reached, power is supplied to the load by controlling
the rectifier, and the DC-DC converter switches from discharging
mode to charging mode.
During commercial power source battery sharing operation mode at
step S56, the charging/discharging determination unit 42 and the
power source control unit 43 periodically calculates the remaining
battery capacity and a load current, calculates an electric current
that may continue to be supplied during the peak time based on the
calculated remaining battery capacity and load current, and perform
`time current control operation mode` in which the present current
is changed into an electric current that may be supplied and an
existing operation continues to be performed during the peak time
at step S59.
After step S59 is terminated or each mode is terminated at each
step, the charging/discharging determination unit 42 determines the
charging state of the battery 30 at step S20 via step S60.
Furthermore, the operation of a single UPS has been described with
reference to FIGS. 7 and 8, for convenience of description, but the
present invention may be applied to two UPSs that operate in
parallel as shown in FIG. 1.
As described above, in accordance with the energy storage system of
the UPS equipped with the battery and the method of driving the
same according to the embodiments of the present invention, there
are advantages in that the utilization of the battery can be
increased and emergency power prepared for a power failure can be
secured through the energy storage operation, some of an
installation cost for the use of the battery can be recovered by a
reduction of energy, and a power reservation ratio for the use of
power can be increased by reducing power during daytime.
Furthermore, in accordance with the energy storage system of the
UPS equipped with the battery and the method of driving the same
according to the embodiments of the present invention, there are
advantages in that power can be further reduced because the battery
capacity is increased in order to increase a power failure
compensation time and the lifespan of the battery can be extended
by reducing the number of times of discharging related to the
lifespan of the battery.
Furthermore, in accordance with the energy storage system of the
UPS equipped with the battery and the method of driving the same
according to the embodiments of the present invention, there are
advantages in that more time for charging the battery after the
battery is discharged during daytime can be increased as compared
with a single UPS because the first UPS and the second UPS are
used, discharging efficiency of the battery can be improved, and
the lifespan of the battery can be extended.
Furthermore, in accordance with the energy storage system of the
UPS equipped with the battery and the method of driving the same
according to the embodiments of the present invention, there is an
advantage in that a power reservation ratio for the use of power
can be increased by reducing power during daytime.
Although some exemplary embodiments of the present invention have
been disclosed for illustrative purposes, those skilled in the art
will appreciate that various modifications, additions and
substitutions are possible, without departing from the scope and
spirit of the invention as disclosed in the accompanying
claims.
* * * * *